Microchips Biotech Inc. designs and manufactures implantable devices based on microchips which include reservoir arrays containing biosensors or drugs. FIG. 1 shows a plan view of sealing grooves and reservoirs in a microchip element 100. The microchip element 100 includes a primary substrate 102 with reservoirs 104, such as microreservoirs. Each reservoir may contain a drug or sensor (neither of which is shown, for simplicity) for controlled in vivo release or exposure, respectively. In order to form a hermetic enclosure about the reservoirs 104, the primary substrate 102 is bonded to a sealing substrate. In this manner, the primary substrate 102 typically includes a number of discrete sealing rings 106 disposed about each individual reservoir 104. The individual sealing rings 106, however, occupy a substantial portion of the surface area of the microchip element 100 and therefore limit the size of the reservoirs 104 and/or limit how closely the reservoirs can be positioned next to one another. That is, the arrangement limits how densely the reservoirs can be packed together in an array. A high density is desirable because it leads to more reservoirs and reservoir contents per volume of the medical implant, and the smaller the medical implant the more tolerable the implanted device is to the patient. It therefore would be desirable to increase the reservoir capacity or area density, while still providing a hermetic seal about the reservoirs and without needing to increase the overall size of the microchip element. It would also be desirable to simplify the fabrication of the sealing structures needed to hermetically seal reservoirs in an array of reservoirs in a microchip element.